General materials and experimental procedures

Acetonitrile (CH₃CN) was purchased from Oceanpak Alexative Chemical Co., Ltd. (Gothenburg, Sweden). Petroleum ether, ethyl acetate (EtOAc), and acetone were analytical-grade from Fine Chemical Co., Ltd. (Tianjin, China). Formic acid was purchased from Kemiou Chemical Reagent Co., Ltd. (Tianjin, China).

Primer synthesis and DNA sequencing were performed by Sangon Biotech Co., Ltd. (Shanghai, China). Plasmid purification kits and agarose gel DNA extraction kits were purchased from Sangon Biotech Co., Ltd. (Shanghai, China). PCR was carried out using a Mastercycler nexus gradient (Eppendorf, Hamburg, Germany) with KOD -Plus- polymerase (Toyobo, Osaka, Japan). In-Fusion® HD Cloning Kit and T4 DNA polymerase were purchased from Takara Bio Inc. (Dalian, China). Other DNA modification reagents were purchased from Thermo Fisher Scientific Inc. (Shenzhen, China).

GC–MS analysis was performed on Thermo Finnigan Trace GC Ultra equipped with a HP-5MS column (0.25 mm i.d. × 30 m, 0.25 μm film thickness) and coupled with Thermo Finnigan Trace DSQ. The temperature of the ionization chamber was 300 °C and the electron impact ionization voltage was 70 eV. The oven temperature began at 75 °C and held for 5 min, then increased to 230 °C at a rate of 20 °C min⁻¹ and stayed at 230 °C for 2 min. It then continued with a second ramp by rising at a rate of 10 °C min⁻¹ to 310 °C and held for 10 min. Helium was used as the carrier gas.

HPLC and LC–MS were carried out on an Ultimate 3000 HPLC system (Dionex) and an amaZon SL ion trap mass spectrometer (Bruker) using electrospray ionization with a Cosmosil 5C₁₈-MS-II column (4.6 mm i.d. × 250 mm, 5 μm; Nacalai Tesque, Inc., Japan). Elution was subjected to a linear gradient [H₂O containing 0.1% formic acid (A) and CH₃CN containing 0.1% formic acid (B); 1 mL min⁻¹; 50%-100% B (0-30 min), 100% B (30–70 min); 208 nm].

UV data, IR data and optical rotations were respectively measured on the JASCO V-550 UV/vis spectrometer, JASCO FT/IR-480 plus spectrometer, and JASCO P1020 digital polarimeter from JASCO International Co., Ltd., Tokyo, Japan. The HRESIMS data were obtained on a Micromass Q-TOF mass spectrometer (Waters Corporation, Milford, USA). 1D and 2D NMR spectra were obtained with Bruker AV 400 and Bruker AV 600 spectrometers (Bruker BioSpin Group, Faellanden, Switzerland) using the solvent signals (CDCl₃: δ _H 7.26/δ _C 77.0; Pyridine-d ₅: δ _H 7.21/δ _C 123.5) as internal standards.

The semi-preparative HPLC was performed on an Ultimate 3000 HPLC system (Dionex) using a YMC-Pack ODS-A column (10.0 mm i.d. × 250 mm, 5 μm; YMC Co., Ltd., Kyoto, Japan). Medium-pressure liquid chromatography (MPLC) was equipped with a dual-pump gradient system, a UV preparative detector, and a Dr. Flash II fraction collector system (Lisui E-Tech Co., Ltd., Shanghai, China). Column chromatography (CC) was performed with silica gel (200–300 mesh, Haiyang Chemical Co., Ltd., Qingdao, China) and ODS (50 μm, YMC Co., Ltd., Tokyo, Japan).